A new, small study provides a tantalizing clue to the causes of autism, suggesting that children with the disorder have heavier brains and an overabundance of brain cells called neurons.
Autism researchers had suspected for more than a decade that the disorder might be the result of abnormal brain growth and development. Previous studies have shown that autistic children have larger heads and brains, and that brain regions crucial for social, emotional, and communication processing are particularly overgrown. But this study is the first to provide hard evidence of brain development gone awry in autistic children, gleaned from actual counts of these brain cells.
In the study, published today in the Journal of the American Medical Association, scientists investigated the brains of 13 boys from age 2 to 16, whose brains were donated for scientific study after they died. Using a precise microscopic technique, the researchers counted the neurons in the brains of these children, seven of whom had autism and six who did not.
They found that the brains of the autistic children had 67 percent more neurons in a region called the prefrontal cortex, an area linked to social, emotional, and communication processing -- functions that are typically lacking in autism.
The brains of the autistic children also weighed an average of 17.5 percent more than the brains of children without the disorder.
Eric Courchesne, the study's lead author and a neurobiologist at the University of California, San Diego Autism Center of Excellence, called these differences "dramatic and surprising."
"We didn't expect to see such a big effect," Courchesne said. "Since the brain doesn't generate new neurons in the prefrontal cortex after birth, we know that this happens during prenatal development. So this points to something going wrong with how the brain initially forms itself in autistic children," he said.
As a baby develops in the womb, the brain typically goes through a boom of neural growth, and the number of neurons nearly doubles during the 10th to 20th week of gestation. This boom is followed by a bust, and half of the cells die away, leaving healthy babies with a normal brain size. Scientists think this cycle allows the brain to organize itself and for neurons to establish connections with each other. But if the brain ends up with an overabundance of neurons, those connections could be disturbed.
"We have lots of functional and anatomic proof that connectivity is the key thing that's disrupted in autism," said Dr. Kate McFadden, a neuropathologist at the University of Pittsburgh Medical Center. "If the numbers of neurons are off, how they link up with other neurons is going to be thrown off."
Many researchers point out that these new findings are very preliminary and don't apply to children and families currently dealing with autism. The study was very small, and currently, there is no way to analyze the brain tissue of living children.
But it does give researchers a tantalizing avenue for future research on the causes of autism. Courchesne noted that studies finding genetic links to the disorder are also crucial to understanding how it develops.
Dr. Lori Warner, director of the HOPE Center for Autism at Beaumont Children's Hospital in Royal Oak, Mich. is hopeful that studies like these could lead to more effective screening and treatment for the disorder.
"If we know what has gone wrong in the development, then we have a better idea of how to screen kids for autism, and how to treat them," Warner said.